Annealing box



Dec. 8, 1936.

P. E. HUNTER ET AL ANNEAL ING BOX Filed Sept. 14, 1935 2 Sheets-Sheet lDec. 8, 193%. P. E. HUNTER ET AL 2,063,603

ANNEALING BOX Filed Sept. 14, 1935 2 Sheets-Sheet 2 l S IniTia) Lenglhof 778 Q SYressed 77'e and Chord lengih et Choral Lengih Patented Dec.8, 1936 ANNEALING BOX Percy E. Hunter and Kenneth J. Deahl, Pittsburgh,Pa.; said Deahl assignor to said Hunter Application September 14, 1935,Serial No. 40,602

Claims. (Cl. 263-49) Our invention relates to annealing boxes adapted tobe employed in the heat-treatment of metals.

Annealing boxes employed in the art are usual- 5 ly the cast metal typeor the sheet metal plate type, composed of plates joined at their edgesto form a unitary box structure. The boxes are, of course, subjected tohigh temperature conditions with alternate periods of heating and cool-],0 ing. One of the main difficulties with such boxes is that the topssag and the sides bulge or otherwise become so distorted to such anextent that they will no longer accommodate a desired charge of materialto be treated or be capable of being placed in the furnaces. They are,therefore, useless for their intended purpose and must be scrapped aftera limited number of heats.

Various devices and artifices have been employed to reduce distortionand maintain the 9 shape of the boxes. For example, internal supportingframework has been used to support the walls and tops of the boxes, butthe framework is so massive and heavy as to materially reduce the chargecapacity of the boxes while increasing the oxidizing volume of air inthe boxes. Also, intricate forms of reinforcing and strengtheningprovisions have been utilized in attempting to increase the life of theboxes, but materially add to the cost of the boxes.

One of the principal objects of our invention is to provide means forrestoring an. annealing box to approximately its original shape duringthe cooling period thereof.

Another object of our invention is to provide means disposed interiorlyof the box and of such form as not to reduce the charge capacity of thebox while maintaining the clearance of air space at a minimum, andoperative to support the top and sides of the box during a heating 4cycle or period thereby preventing excessive distortion and effective torestore the box to its initial shape during the cooling period.

A further object of our invention is to provide means of generallysimplified and improved form for regulating the shape of the box toincrease I on the line IIII of Fig. 1; Fig. 3 is a fragmentary sectionalplan view of the box; Fig. 4 is a View, on an enlarged scale, taken onthe line IVIV of Fig. 3; Fig. 5 is a cross-sectional view of the topportion of a modified form of box; Fig. 5 6 is a diagrammatic viewillustrating the manner of setting up counteracting distorting stressesin the top portion of the box; Fig. 7 is a view similar to Fig. 5, butshowing another modification; Fig. 8 is a modification showing a flat 10top annealing box; Fig. 9 shows still another modification, and Fig. 10is a view taken on the line XX of Fig. 9.

Referring first to Figs. 1 to l, the box is shown as provided with anarched roof or top and may 15 be suitably formed of cast metal or formedof plates welded together at their abutting edges to produce a unitarybox structure. We have shown the box formed with reinforcing grooves orchannels up the sides and across the top of the box that are in' efiectcontinuous, and permit of longitudinal expansion and contraction.

Disposed interiorly of the box and extending transversely thereof is aseries of tie rods or bars I0, each bar having its end secured to theadjacent side wall I I of the box, as by means of plates I2 welded tothe bar I0 and the side of the box II, respectively. The tie bars arearranged in pairs and spaced apart in directions longitudinally of thebox. Each pair of tie bars are arranged at opposite sides of the groovesformed in the walls of the box and preferably are connected to the sidesof the box at the points of juncture between the sides and the top ofthe box. Thus, the charge capacity of the box is not reduced.

Intermediate the ends of each tie bar Ill, an upright strut member I3 isprovided, the lower end of the strut I3 being Welded to the tie bar. Aconnecting bar I4 extends between the struts I3 01 each pair of tie barsIll and is secured at its ends to the upper ends of the struts I3,preferably by welding. The ends of the connecting bar I4 extend throughthe adjacent strut I3 and slidably engage in U-shaped cup members I5that are welded to and depend from the top I6 of the box. The connectingbar I4 and the struts I3 engage the top of the box to support the samebut are not connected thereto, and, therefore, do not add to the weightof the roof.

The tie bars I0 may be initially placed under stress, so as to operateas tension members to restrain the side walls against bulging due to theweight of the top and loss of strength at elevated temperatures and tosupport the roof through 55 the struts l3 against sagging. Since the tierods and strut members are disposed interiorly of the box they will notincrease in temperature as rapidly as the box metal. Under increase intemperature, the. box being restrained by the tie rods ID, the topthereof will expand upwardly, expansion of the ties and struts laggingexpansion of the box. Under elevated temperature, the top may movedownwardly into engagement with the struts and their connecting bars,the bars being bent downwardly slightly, in tension, to a point toeffect stability of the box. During cooling, contraction of the boxleads the contraction of the bars ill, but due to the lever advantage ofthe tie bars over the top [6, when normal temperature is reached the boxis returned to substantially original shape.

The tie bars In, the struts I3, and the connecting bars M are in effecta truss structure for supporting and maintaining the shape of the boxduring the heating and cooling periods. The tie bars and struts arepreferably composed of metal having a higher tensile strength andexpansion and contraction rate than that of the material of the box.That is, we prefer to employ in the supporting structure and in the boxany two metals of diiferent heat expansion, or metals having differentcoefficients of expansion.

For example, a metal such as mild steel, having a given rate ofexpansion may be employed in the box structure While another metal, suchas alloy steel, having a higher rate of expansion may be employed in thesupporting structure. Or two alloy steels of different coefficients ofexpansion may be employed.

Initial stressing of the tie bars may be effected in one manner bymaking the. length of the tie bars equal to the chord distance of thetop I6, heating the box to a temperature sufliciently high to produceloss of strength in the top and plastic slumping thereof to tension thetie bars, the temperature being suificiently low as not to produce lossof strength in the ties. Or, as shown graphically in Fig. 6, the lengthof the ties A initially is made less than the free chord length B of thetop of the box. The chord length is then shortened by pressure appliedexternally to the sides of the box and the ends of the ties welded tothe box. Removal of such pressure produces the desired stress in theties, the box assuming the position indicated by the broken line C.

During the heating up period, expansion of the box leads the expansionof the supporting structure, the top I6 expanding upwardly. Since theties I have a higher expansion rate per unit temperature rise than thebox, they elongate to prevent development of too great stress thereinand, at some temperature, the expansion of the ties will approximatelyequal the expansion of the top plus the initial deformity of the top.Until reaching such temperature, the ties will constantly be maintainedin tension.

We prefer that such temperature be the upper temperature to which thebox will be heated and be approximately 1570F. To this end, mild steelwith a coefficient of expansion of .000006" per degree F. may be used toform the box. Alloy steel having an expansion coefiicient in the rangebetween 1.16 and 1.84 times that of mild steel may be employed for thesupporting structure.

For a box 42 inches in width, maximum temperature 1570 F., and normalroom temperature of 70 F., the total expansion of the box composed ofmild steel would be .378 inch. Total expansion of the ties composed ofalloy steel having an expansion coefiicient of 1.25 times that of mildsteel would be .473 inch. However, to maintain the ties under tension,they are initially shortened to a degree such as tension therein willnot disappear until maximum temperature is reached and, thus, the amountof shortening is made equal to the difference in total expansion atmaximum temperature, or .095 inch. The length A of the ties is,therefore, initially 41.905 inches.

At maximum annealing temperature, any tendency of the top to collapse,creep or sag tensions the tie. bars Ill to the point of stability, andthey support the top and prevent excessive bulging of the sides.

During the cooling period, the greater rate of contraction ofthe tiebars develops the initial tension of the ties when the point of normaltemperature is reached, thereby drawing in the sides and forcing the topupwardly to its original position if there has been any excessivedeformation thereof.

Not only are the tie bars and their strut members of alloy steel able torestore the. box to substantially its initial shape, but are extremelyefiective to support the box against excessive deformation at hightemperatures because of their relatively greater strength at annealingtemperature than that strength possessed by the metals forming the box.

Referring now to Fig. 5, the box 20 is provided with an arched roof notcontinuously curved as in the roof l6, and may be of greater span. Tiebars 2 I, similar to the tie bars ID, are secured at their ends to thepoints of juncture between the roof and the sides of the box. Amedially-disposed triangular supporting member 22 is welded to each tiebar and engages the roof and affords vertical and diagonal supporttherefor. The tie bars 2| and their members 22 are composed 01' metalhaving a higher tensile strength and higher expansive coefficient thanthe metal of the box. In this construction, also, the tie bars may beini-- tially stressed and tension maintained therein during an annealingcycle or operation.

In Fig. '7, for boxes of great width or for additionally supporting theroof thereof against collapsing, we provide an internally-disposed rooftruss composed of chord tie bars 25, an intermediate vertical strut 26,a top compression member 21 and diagonal brace bars 28. All of thevarious bars are. composed preferably of alloy steel and are weldedtogether to form a unitary truss, and the only point of rigid connectionbetween the truss and the box being at the ends of the tie bars, suchends being welded to the box at points of juncture between the top andsides.

The compression member 21 engages the roof only at points spacedlongitudinally of the truss, whereby transfer of heat from the top tothe truss member by conduction is reduced to a minimum and preventsheating of the truss too rapidly.

The top is free to expand upwardly away from the member 21, and anysagging of the roof at annealing temperatures will be arrested by thetruss, thereby preventing excessive deformation of the box.

Not only may light gauge sheet metal be employed to form the boxes tolower the cost thereof, but they will be maintained against excessivedeformation and efiectively reinforced by the alloy steel supportingstructure operative to restore the boxes to their proper workingcondition.

Various features of the invention are capable of use also with annealingboxes having flat tops,

as shown for example in Fig. 8. In this structure, the box top issupported from sagging by a tie bar 3| and a strut 32, the tie bar 3|being preferably of a metal which has a different coefficient ofexpansion than the metal of the box. The strut 32 will prevent the roofexpanding in a downward direction, when subjected to heat, and will, ofcourse, prevent sagging.

In Figs. 9 and 10, we show a beam-like truss of alloy steel forsupporting the top against excessive sagging, and comprises an anglemember 34 disposed beneath the top 35. The flange 36 of the angle memberis welded at its ends to the sides of the box adjacent to the points ofjuncture with the top and serves as a tie member.

The web portion of the member 34 has its upper edge 31 cut away toconform with the contour of the top and is disposed in spaced relationthereto. Seating blocks 38 are preferably welded to opposite sides ofthe web portion of the member 34 in position tosupportingly engage thetop 35. The spaced relation of the top and the upper edge 31 of thetruss member 34 prevents too rapid heating of the truss member while theoppositely-arranged blocks 38 maintain the truss perpendicular to thetop wall of the box.

We claim as our invention:-

1. An annealing box having sides, ends and a roof formed of metal, a tiebar within the box and having its ends welded to opposite sides of thebox adjacent to the points of juncture thereof with the roof, anupwardly-extending strut carried by said tie bar intermediate its endsin position to supportingly engage the roof, and means depending fromthe roof and slidably engaging the upper end of said strut, formaintaining said strut against lateral shifting movement.

2. An annealing box having sides, ends and a roof formed of metal, apair of tie bars arranged in side-by-side relation with the box andhaving their ends welded to opposite sides of the box adjacent to thepoints of juncture thereof with the roof, a strut carried by each tiebar intermediate its ends, in position to supportingly engage the roof,a connecting bar joining the said struts, and means depending from theroof and slidably engaging the upper end of said strut, for maintainingsaid struts against lateral shifting movement.

3. An annealing box of sheet metal having sides and a convex top, thetop being of such thinness that it is not self-sustaining at annealingtemperatures, and a self -contained truss having only abuttingengagement with the underside of the top and secured at its ends to thebox, at the lines of juncture between the top and said sides.

4. An annealing box having a top formed of sheet metal and sides joinedthereto, a tie bar disposed interiorly of the box and having its endssecured to opposite sides of the box, adjacent to the lines of juncturebetween the sides and the top, and a strut carried by said tie barintermediate its ends, in position to supportingly engage the top, thesaid strut having only abutting engagement with said top.

5. An annealing box having a top formed of sheet metal and sides joinedthereto, a tie bar disposed interiorly of the box and having its endssecured to opposite sides of the box, adjacent to the lines of juncturebetween the sides and the top, and a plurality of struts carried by saidtie bar, in position to supportingly engage the top at points to eachside of the longitudinal center line of the top, the said struts havingonly abutting engagement with the said top.

PERCY E. HUNTER. KENNETH J. DEAHL.

